Slide : 1 2-4 November 20082 nd International SpaceWire Conference in Nara, Japan SpaceWire Standard...

2-4 November 2008 2nd International SpaceWire Conference in Nara, Japan Slide : 1

SpaceWire Standard Evolution

Martin Suess

European Space Agency,

E-mail: martin.suess at esa.int,

2-4 November 2008 2nd International SpaceWire Conference in Nara, Japan

Slide : 2


Overview

• Introduction

• Proposed updates to the SpaceWire Standard on:

– Physical Level,

– Character Level,

– Exchange Level,

– Network Level.

• Conclusion


Slide : 3


Introduction

• The SpaceWire standard ECSS-E-50-12A was first published in 2003.

• Since then many groups all over the world worked on the development of SpaceWire links, nodes, routers and networks and on the application of this technology in space systems.

• In the past years the standardization effort aimed at higher level communication protocols such as RMAP.

• In parallel the SpaceWire Working Group is discussing new concepts and additional protocols like SpW-PnP and SpW-RT.

• Through the experience gained with real systems and through the development of new concepts several issues have been identified to be considered for the update of the standard.

• This presentation summarizes updates to the SpaceWire standard which have been proposed during the past years in the SpaceWire Working Group.


Slide : 4


Cable Specification

• The standard provides a detailed specification of the construction of the cable.

• The disadvantage is that the standard does not provide freedom to optimise the cable for specific applications.

• The update should only specify some physical and electrical parameters like:– Differential Impedance,– Signal Skew, – Return Loss, – Insertion Loss, – Near-end Crosstalk (NEXT)– Far-end Crosstalk (FEXT)

Conductor 28 AWG(7 x 36 AWG)Insulating layer

Twisted pair

Inner shield aroundtwisted pair (40AWG)

Outer shield (38AWG)

Outer Jacket

Filler

Filler

Jacket

Binder

Section though a SpaceWire cable as defined in the standard


Slide : 5


Connectors

• The SpaceWire connector is anine-pin micro-miniature D-type.

• It is compact and available for space use.

• D-type connectors do not match the 100 Ω differential impedance.

• Distortion introduced by connectors is acceptable in most cases.

• Other connectors have been proposed and investigated:– Circular 13 pin 38999 Series II

connector,– 4-way twinax connector.

38999-series connector

4-way Twinax connector

micro-miniature D-type connector


Slide : 6


Cable Assembly

• The micro-miniature D-type connector has nine signal contacts. • Eight contacts are used for the 4 twisted pair cables and one is

used to terminate the inner shields at end of the cable from which the signals are being driven.

• The inner shields are isolated from one another. • This prevents a direct ground connection via the SpaceWire link

and provides a symmetrical cable. • A problem occurs when the cable is broken into several parts

due to bulkhead connectors.• In this case the inner shields on both sides of the bulkhead are

not connected to the ground of either side.• A connection of the inner shield on both sides with the

possibility to implement a controlled capacitive decoupling on one side behind the plug could be investigated.


Slide : 7


Distributed Interrupts

• Two control flags of the time-codes are reserved for future use.

• It has been proposed to use one of the reserved states to distribute interrupts through the network.

• They will propagate on the same side channel as time-codes independent of the normal traffic.

• This mechanism will allow to define 32 Interrupts Codes and 32 Interrupt-Acknowledge Codes.

• Routers and nodes propagate the interrupts only once unless:– a timeout has expired– they have received the corresponding Interrupt-

Acknowledge Code


Slide : 8


Distributed Interrupts

• Interrupt-code: interrupt request, IRQ vector I=16h

Node 82Master

Router 1

Router 2

Router 3Node 74Master

Node 64 Slave

Node 60Slave

• Interrupt Acknowledge: interrupt acknowledgment

I=16h

I=16h


Slide : 9


Multi-Time-Code Master Mechanism

• Only one node in network is allowed to act as time-code master.

• It is the only to should provide the active TICK_IN signal which triggers the broadcast of the Time-Codes.

• This is required to avoid collisions of Time-Codes within the network.

• For fail safety and redundancy reasons it could be useful to have simultaneous Time-Codes from different time-code masters in a system.

• Up to two additional time signals could be implemented by using the two remaining reserved states of the control flag.


Slide : 10


Simplex Link Operation

• Many high speed payload data applications require only a simplex connection.

• This could be for example a direct connection from a high rate instrument to the memory.

• For these simple applications the back of SpaceWire is sometimes regarded as complex and of cable mass.

• A proposal has been made to modify the SpaceWire codec and the state machine to support simplex operation.

• Also the possibility of a half-duplex SpaceWire implementation has been suggested.

• The details and consequences of these proposals remains to be investigated.


Slide : 11


2 Mbit/s Link Speed at Start-up

• The standard currently requires a link speed of 10 Mbit/s at start-up.

• In some applications data rates of less than 2 Mbit/s are required.

• For power saving and simplicity reasons the start-up at 2 Mbit/s is desirable for these systems.


Slide : 12


Configuration Port 0 in Nodes

• SpaceWire routing switches have an internal configuration port with address zero.

• It is used to configure the routing switch and to access status information.

• This is an important feature for network discovery and PnP.

• Currently this port zero is only required in routing switches and not in nodes.

• It is intended that in the update the definition of SpaceWire Node addressing will be aligned with the SpaceWire Routing Switch.


Slide : 13


Configuration Port 0 in Nodes

1st Byte

ConfigurationEngine,PnP1st Byte = 0

1st Byte = 32-254 => LA

1st Byte = 1 - 31

Application LevelSoftware

PID analysis,Transport protocol identification.

Reserved

Payload PID LAPath Address

EOP


Slide : 14


Router Function in Nodes

• What has been described before corresponds to a very simple router with:– one external port,– one internal configuration port and – one node internal port.

• This concept can be extended to several external ports by introducing path addressing and a routing table.

• This would fulfil the needs of network discovery • Could provide an elegant method for cross strapping

and redundancy switching• Enable easy packet routing through nodes.


Slide : 15


Conclusion

• A non exhaustive list of the modifications proposed to the SpaceWire standard has been presented.

• Additional proposals are welcome and can still be submitted to the author.

• The different options will be discussed and consolidated within the SpaceWire working group starting next year.

• In many cases breadboard implementations of the modifications already exist.

• Results of the discussions on modifications will be included in the next update of the SpaceWire standard.

• The review and update of the SpaceWire standard is planned to be started in 2010.

Slide : 1 2-4 November 20082 nd International SpaceWire Conference in Nara, Japan SpaceWire Standard...

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